Since the announcement of a laminated organic electroluminescence (hereinafter, sometimes simply referred to as “EL”) element using a vapor deposition process by Kodak Corp., development of an organic EL display and an organic EL lighting is being aggressively made, and an organic EL display and an organic EL lighting are now used in practice.
In such a laminated organic electroluminescence element, plural organic layers (for example, a luminescent layer, a hole injection layer, a hole transport layer and an electron transport layer) are provided by stacking the layers between an anode and a cathode. In many cases, the organic layer is formed by vacuum depositing an organic layer material such as low molecular dye. However, it is difficult to obtain a homogeneous defectless thin film by a vacuum deposition process. Furthermore, since the vacuum deposition process requires a long time to form plural organic layers, a problem to be solved exists also in view of manufacturing efficiency of the element.
In this connection, a technique where plural organic layers of a laminated organic electroluminescence element are formed by a wet film formation method has been reported. For example, Patent Document 1 describes an organic electroluminescence element having a luminescent layer and a crosslinkable polymer-containing charge transport film obtained by coating a composition containing a compound having a crosslinking group and crosslinking the composition by light or heat. When a crosslinkable polymer-containing charge transport film is used, other layers can be easily formed on the charge transport film by a wet film formation method.
Such a process of manufacturing an organic electroluminescence element by a wet film formation method is expected to enable a simple, efficient and inexpensive manufacturing of a large-area organic EL device, and various studies are being made thereon. Also, in the process of manufacturing an organic electroluminescence element by a wet film formation method, the wet film formation can be performed by using an inkjet system, a nozzle coating system or the like as described in Patent Documents 2 and 3, and this is considered to enable the realization of a low-cost, large-area organic EL device.
In the process of manufacturing an organic electroluminescence element by a wet film formation method, materials for forming a layer having various functions are dissolved and dispersed in a solvent to produce an ink, and a coated film is formed by using the ink. However, in such an ink, precipitation, aggregation, crystallization and the like of the solute sometimes occur in the period until use.
Considering this, at the manufacture of an organic electroluminescence element including a wet film formation process, the ink is filtered immediately before the ink is used in practice (see, Patent Documents 4 to 8).
In this way, the manufacturing technology of an organic electroluminescence element by a wet film formation method is expected to be useful for realizing a simple, efficient and inexpensive process and forming a large-area element, and various developments have been conventionally made. As for the organic electroluminescence element manufactured by a wet film formation method, an element having a longer drive life and a higher current efficiency is demanded.